THS4021_16 Datasheet, PDF (9/29 Pages) Texas Instruments – 350-MHz LOW-NOISE HIGH-SPEED AMPLIFIERS

THS4021
THS4022
www.ti.com
SLOS265C – SEPTEMBER 1999 – REVISED JULY 2007
APPLICATION INFORMATION
Theory of Operation
The THS402x is a high-speed operational amplifier configured in a voltage feedback architecture. It is built using
a 30-V, dielectrically isolated, complementary bipolar process with NPN and PNP transistors possessing f_T of
several GHz. This results in an exceptionally high-performance amplifier that has a wide bandwidth, high slew
rate, fast settling time, and low distortion. A simplified schematic is shown in Figure 30.
(7) V_CC+
IN– (2)
(6) OUT
IN+ (3)
NULL (1)
NULL (8)
Figure 30. THS4021 Simplified Schematic
(4) V_CC–
S0276-01
Noise Calculations and Noise Figure
Noise can cause errors on very small signals. This is especially true when amplifying small signals, where
signal-to-noise ratio (SNR) is very important. The noise model for the THS402x is shown in Figure 31. This
model includes all of the noise sources as follows:
• e_n = Amplifier internal voltage noise (nV/√Hz)
• IN+ = Noninverting current noise (pA/√Hz)
• IN– = Inverting current noise (pA/√Hz)
• e_Rx = Thermal voltage noise associated with each resistor (e_Rx = 4 kTR_x)
Copyright © 1999–2007, Texas Instruments Incorporated
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